Method of manufacturing piezo crystals



Nov. 30, 1948. w. l. CRONAN 2,454,777

METHOD OF MANUFACTURING PIEZO CRYSTALS Filed Dec. 26, 144

IN V EN TOR. W417i 1. CFO/WIN Patented Nov. 30, 1948 METHOD OF MANUFACTURING PIEZO CRYSTALS Walter Irving Cronan, New York, N. Y., assignor to Federal Telephone and Radio Corporation, New York, .N. Y., a corporation of Delaware Application December 26, 1944, Serial No. 569, 745

6 Claims.

The invention relates to a method :of manufacturing piezo crystals and particularly crystals of different frequency characteristics.

The entire process of manufacturing piezo crystals involves a great number of steps starting with weighing, cleaning, sorting, and grading raw quartz, whereupon the raw quartz is cut to wafers which are divided into crystal blanks. This comprises only the most important steps, since many inspection steps and other procedures are necessary if usable crystals are to be produced. A plurality of crystal blanks is then .piled up one above the other to form a loaf which has the shape of a block ground on all four sides to a certain size of its base in accordance with the frequency desired.

In order to provide crystal blanks of different predetermined frequency characteristics it previously was necessary to grind as many loaves as crystals of different frequency characteristics were desired. If, for instance, the daily output of a manufacturing plant contained crystals having 80 to 100 different frequency characteristics, it was necessary heretofore to provide the equivalent number of grinders requiring a tremendous floor space without using these machines to full capacity.

It is an object of the present invention to provide a method of manufacturing crystal blanks of different frequency characteristics by forming a loaf of the previously cut crystal blanks and tapering two sides of the loaf, thus shaping the loaf to a frustum of a pyramid with two sides perpen dicular and two sides at an angle to its base.

It is another object of the present invention to secure the piled up crystal blanks to a rigid block with liquid wax which upon cooling provides a rigid connection for the blanks.

It is still another object of the present invention to subject the loaf to a grinding process in which two sides of the loaf are tapered by mounting a plurality of loaves on a revolving magnetic support tilted to its axle at a predetermined angle in accordance with the desired taper of the loaf. By feeding the support against a revolving grinding device, the axle of which is in a parallel but coaxially displaced position to that of the support axle, a frustum of a crystal pyramid having two sides perpendicular and two sides at a predetermined angle of less than 90 to the base is produced.

It is a further object of the present invention to provide an apparatus for grinding one side of a pile of crystal blanks in a plane less than 90 to the base of the said pile, which apparatus cumprises means for holding the pile together in order to form a rigid block, means for securing the block to a support, means for inclining the face of the support at an angle to a plane normal to the axle, a grinding face which is adapted to move against one side of the pile of blanks, and means for feeding the support against the grinding face.

The invention will be best understood by reference to the following specification and claims and to the illustrations in the accompanying drawings, in which:

Figure '1 is an elevational view of a crystal loaf shown before and after shaping it, in accordance with the present invention;

Fig. .2 is an elevational schematic view of the device for grinding crystal loaves;

Fig. 3 is a front view of the support along the lines 3-3 of Fig. 2, and

Fig. 4 is a schematic view of a part of the support with the loaf in relation to a part of the rinding device.

Fig. 5 is a perspective view of two L-shaped holders of a crystal blank pile containing the crystal block.

As mentioned before, in manufacturing crystal blanks, the raw quartz is first cut into wafers, and after inspection the latter are further out into crystal blanks. Before the second cutting process takes place, the parts of the wafers which show twinning or other faults are eliminated from the finally acceptable crystal blanks. A plurality of crystal blanks are then piled up in the form of a loaf by applying fluid wax to the pile. In the process, as applied heretofore, all four sides of the loaf were then ground to provide a very clear finish, and at the same time, to a cross sectional size according to the desired frequency characteristic of the crystal blanks to be produced. All blanks of the same loaf thus possess the same frequency characteristic.

In the method according to the present invention, two sides only of the loaf are subjected to the grinding process in order to give them a clear finished face. A loaf so prefabricated is first mounted in an L-shaped ferrous holder and secured thereto by applying fluid wax between the surfaces to be connected and allowing the wax to cool until a good bond is effected.

The crystal loaf is then subjected to a grinding process in which two sides of the loaf are tapered as shown in Fig. l in such a way that the blanks .produced at the top of the frustum are of a size equivalent to the highest desired frequency, while blanks at the bottom of the frustum are of a size equivalent to the lowest desired frequency. Thus, according to this method the loaf is shaped to a pyramid comprising a number of crystal blanks, all of which are graduated from the lowest to a highest frequency respectively from the base to the top of the frustum. Upon heating the loaf the wax between the crystal blanks melts away and a number of crystal blanks of predetermined size ranging from a lowest to a highest frequency are produced.

Figs. 2 to 4 of the drawings illustrate how the two sides of a block-shaped loaf can be tapered. A plurality of L-shaped ferrous holders each of which has a crystal loaf 2 mounted thereon is fixed to a magnetic chuck 3 the surface of which is tilted away from a plane normal to the rotating axle 4 by screws or other convenient means. A grinding surface 5, preferably disc shaped, is revolved by means of a shaft 6, which is parallel to axle 4 but coaxially displaced therewith. It is preferred to arrange the ferrous holders in pairs (see Fig. 5) because two crystal loaves support each other by this arrangement during the grinding process. The surface of the magetic chuck 3 preferably is marked with line 'i or similar indicia which are parallel to the tilting axis 8-8 and the ferrous holders on the surface of the magnetic chuck 3 are set perpendicularly to the marking lines '5. The grin-ding surface is rotated preferably by a different motor than that which rotates the magnetic chuck 3. The support [4 is carried by a feeding member is which is provided with inner thread corresponding with the thread of the feeding screw H which is rotated preferably by any known gear transmission (not shown). The feed screw is provided at one end with a handle 18 in order to move the magnetic chuck 3 in contact with the grinding device 5 shaft 3 of the magnetic chuck 3 rotates in a bearing i3 connected to a threaded feeding member l6 adapted to be adjusted by a rotating feed screw i'l having a handle it as in a lathe for example. As shown in Fig. 3, four pairs of crystal loaves 2 are mounted on the magnetic chuck 3 and tapered at the same time, and upon completion of the grinding operation on one side of the crystal loaf, the holders are removed from the magnetic chuck 3, turned around 90 and set again in such a way that the crystal loaves of each pair support each other as shown in Figs.

3 and 5. In the latter figure an L-shaped holder in full lines and the arrangement of the second adjacent holder in point dotted lines is shown in a perspective view for the purpose of better demonstration. Then the second side of the crystal loaf 2 is subjected to the same grinding process which" results in the tapering of the second side of the loaf 2.

When the double grinding process is finished holders 1 are heated, whereupon the paraifin melts off and a number of single crystal blanks are produced which have frequency characteristics ranging from a lowest to a highest frequency as predetermined. All crystal blanks 9 between the top blank and the bottom blank of the frustum are of intermediate frequencies.

In Fig. 4 it is shown diagrammatically that by arranging the magnetic chuck 3 at an angle I!) to the grinding surface 5 the tapering of the crystal loaf 2 can be achieved very easily. As it appears quite clearly in Fig. 1 that the specific crystal blank, Ii, which is closer to the bottomof the frustum, is of larger size and, therefore, of lower frequency than the specific crystal blank 12 near the top of the frustum which is ,of smaller 4 size than the crystal blank II and, therefore, of higher frequency.

As stated, before the grinding device as shown in the drawing is merely one embodiment of a device with which the present method can be performed. A reciprocating type grinder would achieve the same result.

While I have disclosed the principles of my invention in connection with a particular embodiment, it will be understood that such is given by way of example only and not as a limitation of the scope of the invention as set forth in the objects and the appended claims.

What I claim is:

1. The method of manufacturing piezo crystal blanks of different frequency characteristics, comprising the following steps: piling up the said blanks one above the other to form a loaf, joining said piled up blanks to form a rigid block, grinding two of the four sides of the said loaf in a plane perpendicular to the base of the said loaf, grinding the two other sides at a predetermined angle of less than to the base in order to taper the said loaf on two sides to a largest predetermined size on one end and a smallest predetermined size on the other end of said leaf, then separating all of the blanks of the said loaf, thereby producing a blank of lowest predetermined frequency at one end, a blank of highest predetermined frequency at the other end of the loaf, and a plurality of blanks of intermediate fre-- quencies between the said highest and said lowest frequencies.

2. The method of manufacturing piezo crystals of different frequency characteristics, comprising the following steps: cutting raw quartz to wafers, cutting the said Wafers to crystal blanks, piling up the said blanks one above the other to form a loaf, joining said piled up blanks to form a rigid block, grinding two of the four sides of the said loaf perpendicularly to the base of the said loaf, grinding the two other sides at a predetermined angle of less than 90 to the base in order to taper the said loaf on two sides to a largest predetermined size on one end and a smallest predetermined size on the other end of the said loaf, then separating all of the blanks of the said loaf, thereby producing a blank of lowest predetermined frequency at one end, a blank of highest predetermined frequency at the other end of the loaf, and a plurality of blanks of intermediate frequencies between the said highest and said lowest frequencies.

3. The method of manufacturing piezo crystals of different frequency characteristics, according to claim 1, in which the step of grinding the two other sides of said loaf of crystal blanks, comprises mounting a plurality of loaves on a rotating support inclined at an angle to a plane normal to the revolving axle of the said support,

grinding one side of the said loaf by feeding the.

said support against a rotating grinding device, the axes of both the said support and the said grinding device being parallel, then rearranging the said loaves and grinding the second side.

- 4. The method of manufacturing piezo crystals of different frequency characteristics, according to claim 1, in which the step of grinding the two other sides of the said loaf of crystal blanks comprises mounting a plurality of loaves on a rotating magnetic support according to a predetermined'pattern.

5. The method of manufacturing piezo crystals of different frequency characteristics, according to claim 1, which includes the steps of connecting the said piled up blanks to a rigid block in a holder with liquid wax, cooling off the said holder with the said piled up blanks, subjecting the said loaf to the grinding process, and heating the said pile of blanks, whereupon a plurality of blanks of predetermined frequency is produced.

6. The method of manufacturing piezo crystal blanks of different frequency characteristics, comprising the following steps: piling up the said blanks one above the other to form a loaf, joining said piled up blanks to form a rigid block, grinding at least two of the four sides of the said loaf at a predeterminded angle of less than 90 to the base in order to taper said loaf to 2. largest predeterminded size on one end and a smallest predetermined size on the other end of the said loaf, then separating all of the blanks of the said loaf, thereby producing a blank of lowest predetermined frequency at one end, a blank of highest predetermined frequency at the other end of the loaf, and a plurality of blanks of intermediate frequencies between the said highest and said lowest frequencies.

WALTER IRVING CRONAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,092,867 Sellew Apr. 14, 1914 1,377,118 Eaton May 3, 1921 1,933,373 Fraser Oct. 31, 1933 1,990,002 Schafer Feb. 5, 1935 2,136,036 Avery Nov. 8, 1938 2,274,332 Jarrett Feb. 24, 1942 2,354,616 Sanders July 25, 1944 2,354,970 Volkel Aug. 1, 1944 2,375,003 Kent May 1, 1945 2,383,638 Faber Aug. 28, 1945 2,394,610 Hawkins Feb. 12, 1946 2,397,300 Tilton Mar, 26, 1946 

